Kiwi Fabian Coulthard has seen his lead in the Supercars championship dwindle after Chaz Mostert won Saturday's race on the Gold Coast in steady rain and slippery conditions.

Coulthard was handed a 15 second penalty that dropped him to 19th while title rival Jamie Whincup finished sixth to reduce the Shell V-Power Ford driver's lead to 37 ahead of a repeat 300km test on Sunday.

The Supercheap Ford of Mostert and Steve Owen took the chequered flag ahead of Cam Waters and his Kiwi co-driver Richie Stanaway - the latter was impressive charging through the field yet again.

Tim Slade made the most of his Kiwi co-driver Andre Heimgartner's brilliant opening stint to take third place.

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Scott McLaughlin and Alex Premat battled to find much speed in their Shell V-Power Ford and had to settle for 14th while Shane van Gisbergen made up some spots in the second half of the race to secure fourth place.

Coulthard was unlucky to be given the penalty. He turned Nick Percat around after the Holden driver had run wide and came back onto the racing line.

"It was unfortunate," Coulthard said. "We tried our best to get as high as we could in qualifying. The incident with Nick - he had a wobble and I tried to check it up but we made contact. I have to cop it on the chin."

Both Shell V-Power Fords struggled to display the speed they've shown at most tracks this season.

"We are trying as best as we can," a clearly frustrated Coulthard said.

Better conditions are forecast for Sunday's race.

Championship standings
Fabian Coulthard 2479 points
Jamie Whincup -37
Scott McLaughlin -76
Chaz Mostert -121
Shane van Gisbergen -217